LuLu

About

LuLu is a free, open-source firewall for macOS 10.15 and later that blocks unknown outgoing network connections. The site notes that nearly every application makes network connections, and so does malware, so LuLu aims to protect both your privacy and your Mac. During installation, you manually approve its System Extension and Network Filter in System Settings. Its default settings let Apple and already installed programs access the network without alerting you, and you can change these later in LuLu's Settings.

When a new, unauthorized outgoing connection is created, LuLu shows an alert with the name of the process and its destination, and you can block or allow the connection. The alert offers code signing information, a process hierarchy view of the process's origins, and a VirusTotal button that opens scan results in your browser. By default, your decision applies to the whole program. Using the Rule Scope and Rule Duration options, you can instead apply a rule only to a specific remote endpoint, and set it to last always, for the process's lifetime, or until a set time.